This work introduces the ψ-Coherence Profile, a formal retentive diagnostic for identifying structural persistence in the large-scale universe. Using the principles of ψ-Architecture — the retentive stability term Λψ, the vanishing dissipation gradient Δψ → 0, and the persistence of informational invariants Ξ — the paper demonstrates that Euclid DR1 void-boundary shells exhibit a coherence and sharpness unexplained by standard ΛCDM dynamics. The ψ-Coherence Profile provides the first quantitative method for mapping retentive shells, detecting Ξ-nodes, and distinguishing dissipative evolution from structural retention. This framework establishes a new cosmological regime — the post-dynamic universe — where form persists even as flux fades.